How to Get the Binding Energy by Mass Spectrometry

How to Get the Binding Energy by Mass Spectrometry Speaker: Tianyu Sun Advisor: Prof. Wu Dr. Zhang

Preface Empedocles (490–430 BC, Greek) said: “Lovewill bring about the element hate will separate the element” love hate

Preface Binding energy 我做了这么久计算和有机机理，对化学理解就是“能量和电子的分配”

Preface in organometallic reactions, the key reactive intermediates are coordinatively unsaturated transition metal–ligand complexes that have an open site by loss of one or more ligands. These unsaturated intermediates are good catalysts because they are reactive But transient and difficult to study such information would enable predictions of the feasibility of desired reaction

Preface • The methods to get the binding energy: • photoelectron spectroscopy • Timeresolved infrared spectroscopy • ion beam studies of endothermic reactions • flowing afterglow • kinetic energy release distributions • Energyresolved collisioninduced dissociation • 1aser-powered homogeneous pyrolysis • guided ion beam mass spectrometry • Quantum chemistry……

Outline • Kinetic theory of gases • maxwellspeeddistribution • ClassicCollision Theory • cross section • Determination of cross section by MS • threshold energy (阈能) • Determination of Binding Energy • Doppler broadening • the relative velocity distribution • the models of cross section • Equipment • ion beam energy • guided ion beam • pressure • Future work • summary

kinetic theory of gases Ideal gas maxwellvelocity distribution Often we more care about speed, no velocity! v maxwellspeeddistribution v+dv the number of particles with velocity between and + in per unit volume

kinetic theory of gases maxwellspeeddistribution

ClassicCollision Theory ur B θ dAB A b dAB=rA+rB ur is the relative speed between particle A and particle B μ is the reduced mass εcis the threshold energy, if ε’r> εc, the reaction can happen!

ClassicCollision Theory ur B θ dAB A br :reaction radius b define σr the reaction cross section quantum states

Determination of cross section by MS Using mass spectrometer can get the Ion intensities for reaction gas cell Ip(ArH+) + + + + Mass spectrometer + + + + + + + + I0 IR(Ar+) At a low pressure Just single collison P. B. Armentrout,J. Chern. Phys., 83, 166 (1985)

Determination of cross section by MS at low pressure, just single collison first order reaction lis the effective path length n is the density nl t σtot k1

Determination of cross section by MS At low pressure Taylor expansion IR≈(IR+ΣIP)(1- σtotnl) Individual product cross sections σp σp→ threshold energy

Determination of Binding Energy gas cell gas cell high ion beam energy low ion beam energy Elab»kT + + + + + + + + Elab<kT high low target molecule: stationary target molecule: Doppler broadening the σ is a function of Elab the relative velocity is important

Determination of Binding Energy how to get the relative velocity? M target molecule m V v(cm) v center of mass(cm) M Vcm V0(cm) m V0 monoenergetic ion beam if v=0 E0 is nominal center of mass energy

Determination of Binding Energy the thermal distribution of v gives rise to a distribution of V velocity space ρ: the volume of the red area to the volume of the whole shell of radius v dV0 dv V v V0 V0+V θ V0-V G. J. SCHULZT, PHYS.REV., 32, 110 (1954).

Determination of Binding Energy the ratio of particles with relative velocity between V and V+dV

Determination of Binding Energy integration gives: It is convenient to introduce the parameters

Determination of Binding Energy relative kinetic energy disturbution convolution of σ(E) σapp(E0) is the apperent reaction cross section + + + + The (E/Eo)1/2factor accounts for the difference in the residence times of ions in the interaction region at different ion energies. gas cell low ion beam energy Elab<kT low target molecule: Doppler broadening P. B. Armentrout,J. Chern. Phys., 83, 166 (1985)

Determination of Binding Energy σ(E) is a function of threshold energy classic quantum the models of σ(E): Exponential Cross Section Linear Cross Section Inclined Step-Function Cross Section Step-Function Cross Section

Determination of Binding Energy σ0is a scaling factor E the relative kinetic energy n an adjustable parameter quantum states (vibrational, rotational, and electronic) with energies Eiand populations gi The σ0,n, and E0 parameters are fitted byleast squares analysis E0 is nominal center of mass energy CRUNCH L-CID Peter Chen, J. Phys. Chem. A, Vol. 111, No. 30, 2007

Determination of Binding Energy threshold energy there are three types of reaction used to determine the binding energy of M+–L

Equipment monoenergetic ion beam V0 gas cell The energy spread of Elab need to be very narrow Because the cross section is a funtion of energy + + + + Elab momentum analyzer serves to narrow the energy spread The narrower , the better P. B. Armentrout,J. Chern. Phys., 83, 166 (1985)

Equipment The scattering can reduce the signal + + detector detector + + So we need to trap the ionic products regardless of scattering angle. + +

Equipment Using octopole to trap the ion Travelling wave (T-wave) ion guide adjacent rings have opposite phases of radio frequencevoltage the effective potential

Equipment At a low pressure, Just single collison gas cell + + + + 2.25e-2 Pa Pressures 6.5e-6 Pacan be used for cross section measurements.

Future research Pd II-Catalyzed Enantioselective Activation of C(sp2)-H and C(sp3)-H Bonds Using Monoprotected Amino Acids as Chiral Ligands Yu, J.-Q.Angew. Chem. Int. Ed. 2008, 47, 4882.)

Summary Determination of Binding Energy threshold energy Equipment

Thanks for your attention

How to Get the Binding Energy by Mass Spectrometry